In a hybrid construction machine, it has been known that a lack of output with miniaturization of an engine is compensated by a generator motor to improve fuel consumption. A state of charge of an electric storage device which supplies power to a motor generator that conducts the assist of an engine output, has been set to be a predetermined state of charge during a target operating time.
When, however, the work of a load heavier than intended work is continuously done, there occurs a situation in which an actual state of charge falls below a state of charge prescribed as a target. Thus, when the work is continued in a state in which the actual state of charge is on the level lower than the target state of charge, an engine assist is disabled due to the lack of the state of charge when an engine assist operation is performed by a generator motor, so that an engine stall occurs.
A prior art capable of solving such problems has been proposed in a Patent Document 1. A drive control device according to the prior art is equipped with a state-of-charge detecting means which detects a state of charge. The drive control device determines a specific operation mode on the basis of a predetermined operation of a hydraulic operating part and suppresses a power running assist corresponding to the state of charge using this operation mode as a judgment criterion, thereby preventing rapid decreases in the state of charge.